Low loss passband-tunable flexible metasurface with polarization-insensitive and angle-stable characteristics

• Tunability of Passband: Continuous tuning achieved via varactor diodes integration from 2.7 to 3.4 GHz (IL < 3 dB). • Broadband Rejection: Superior out-of-band rejection (IL > 15 dB) across a wide frequency range of 4–18 GHz. • Design for Flexibility: The fabricated prototype on a flexible substrate demonstrates excellent mechanical flexibility and performance stability under oblique incidence up to 60° for both TE and TM polarizations. • Mechanism Validation: We provide a comprehensive Equivalent Circuit Model (ECM) that accurately predicts the operating mechanism. This paper presents a low loss passband-tunable polarization-insensitive metasurface with angle-stable out-of-band rejection. The proposed design incorporates meandering slots into conventional rectangular patch structures and utilizes interlayer coupling capacitance to achieve both element miniaturization and a selective filtering response. The resonance frequency is dynamically tuned via varactor diodes, which are biased through an integrated network formed by the underlying grid structure and a metallic via. An equivalent circuit model (ECM) is developed to investigate the operating mechanism. Simulation results demonstrate an insertion loss (IL) below 3 dB across the 2.7–3.4 GHz tuning range, along with out-of-band rejection exceeding 15 dB from 4 to 18 GHz under both transverse electric (TE) and transverse magnetic (TM) polarizations. A prototype was fabricated and the measured results under normal and oblique incidence show excellent agreements with simulations, which experimentally verifies that the proposed metasurface simultaneously supports passband tunability and angle-stable out-of-band rejection